The visible absorption in cyanine dyes has been addressed both experimentally and theoretically. Calculations performed at the time-dependent density functional theory level reproduce the variations of the maximum of absorption with the chemical structure. A linear scaling procedure is however required to achieve an accuracy of about 10 nm and this accuracy is increased when the calculations take into account the effects of the solvent using the integral equation formalism of the polarizable continuum model. Improved agreement between theory and experiment will however require an appropriate treatment of the vibronic structure. (c) 2006 Elsevier B.V. All rights reserved.